Remote Sensing and Geophysical Investigations of Glacial Buried Valleys in Northeastern Kansas

Aquifers found in glacial buried valleys are a major source of good-quality ground water in northeastern Kansas. The extent and character of many of these deposits are not precisely known, so a detailed study of the buried valleys was undertaken. Test drilling, Landsat imagery, shallow-earth temperature measurements, seismic refraction, surface electrical resistivity, and gravity data were used to evaluate two sites in Nemaha and Jefferson Counties. Tonal patterns on springtime Landsat imagery and winter/summer anomalies in shallow-earth temperatures were quick and inexpensive methods for locating some glacial buried aquifers and suggested areas for more intensive field studies. Reversed seismic refraction and resistivity surveys were generally reliable indicators of the presence or absence of glacial buried valleys, with most depth determinations being within 25% of test-drilling results. The effectiveness of expensive test-hole drilling was greatly increased by integrating remote sensing, shallow-earth temperature, seismic, and resistivity techniques in the two buried valley test areas. A gravity profile allowed precise definition of the extent of one of the channels after the other techniques had been used for general information.     

Sedimentary evidence for an archaean shallow-water volcanic-sedimentary facies,Eastern Pilbara Block,Western Australia

Sedimentological studies of the dominantly volcanic, ca. 3.5 b.y. Warrawoona Group, eastern Pilbara Block, Western Australia, indicate widespread shallow-water deposition. Many cherty metasediments within the ultramafic-mafic sequence represent silicified carbonate mud, sand, breccia and conglomerate, and show cross-lamination, ripple marks, scour-and-fill structures, and evidence of reworking. At North Pole, some cherty metasediments appear to be silicified and baritized gypsiferous evaporites, and contain microfossils. Felsic volcaniclastic rocks include pyroclastic deposits, cross-laminated tuffaceous metasediments and conglomerate. Subaerial volcanism apparently increased as deposition proceeded.The depositional basin was large, volcanically active and apparently shallow with subdued marginal relief. Felsic volcanoes formed topographic highs within the basin from which sheets of volcanically derived sediments interfingered with ultramafic-mafic volcanics. The Onverwacht Group of the Barberton Mountain Land, South Africa, is of similar age to the Warrawoona Group and probably represents a similar environment, but other greenstone belts may have formed in contrasting basins, possibly under differing tectonic regimes.     

The Activity of Liaocheng-Lankao Buried Fault During the Quaternary——An Important Buried Active Fault in the Eastern China Plain

On the basis of locating by the geochemical prospecting,shallow seismic sounding,drilling,geological profiling,and neogeochronological dating,we first found out the dislocation amount along the Liaocheng-Lankao buried fault since the Quaternary and the age of its latest activity phase and determined that the upper break point by the fault dislocation reaches 20m below the surface,The latest activity phase was in the early Holocene and the Fault is a shallow-buried active fault.An average dislocation rate along the fault is 0.12mm/a since the Quaternary.Thus,it is a buried active fault with intermediate to strong movement strength in the eastern china.     

基于GIS/RS的洪湖东分洪区洪水风险制图

本文计算了洪湖东分洪区洪灾损失.洪水风险带以模拟的洪水淹没深度表示.这是洪水风险综合评价模型的基础.本项研究基于GIS为基础的水动力模型计算洪水淹没深度;并以GIS/RS为基础建立了单位洪水风险评价模型,计算不同洪水风险带的直接损失.研究表明,综合洪水风险评价模型在长江流域应用是可行的.     

Mapping a Brine Plume Using Surface Geophysical Methods in Conjunction with Ground Water Quality Data

Oil field brine was applied to a gravel roadbed at an instrumented study site in Newark, Ohio, to simulate the use of brine as a deicer on roads in certain areas of Ohio. Brine was applied on a weekly basis eight times during the winter of 1988 as part of the deicing simulation. Eleven wells were installed at the site prior to brine application to permit collection of ground water quality samples. Surface geophysical methods — electrical resistivity and electromagnetic conductivity — were used to map the resulting brine plume. The accuracy of the methods was evaluated by comparing geophysical and ground water quality data. The presence of brine in ground water resulted in a decrease in resistivity and an increase in conductivity. Specific conductance measured in the field was used as a general indicator of the presence of the brine plume in ground water. Chloride concentration was an indicator of brine in the ground water. Results of the surface geophysical surveys correlated best with chloride and dissolved solids concentrations, and with specific conductance in ground water. The surface geophysical methods were found to be useful for qualitative interpretations of ground water quality changes resulting from the application of brine on roads.     

物探方法在临清坳陷某区块山西组沉积相分析中的应用

临清坳陷某区块缺少岩心、薄片、录井及常规测井资料。为了研究其目的层山西组沉积相对储层的控制作用,指导非常规天然气的高效开发。通过利用较少的录井岩性统计资料,结合地震物探方法,分析地震剖面特征、优选地震均方根振幅及相对波阻抗属性,确定该区目的层沉积相。通过上述地震属性研究的物探方法,确定山西组储层为河控浅水三角洲相和碳酸盐台地相,主要发育分流河道、分流间湾及局限台地沉积微相。其中三角洲相是主要的沉积相类型,分流河道是有效储层发育的主要微相类型。     

Geophysical Investigation of Fresh‐Saline Water Interface: A Case Study from South Punjab,Pakistan

The importance of the study of fresh‐saline water incursion cannot be over‐emphasized. Borehole techniques have been widely used, but they are quite expensive, intrusive, and time consuming. The electrical resistivity method has proved very successful in groundwater assessment. This advanced technique uses the calculation of Dar‐Zarrouk (D‐Z) parameters, namely longitudinal unit conductance, transverse unit resistance, and longitudinal resistivity has been employed by using 50 vertical electrical sounding points to assess the groundwater and delineate the fresh‐saline water interface over 1045 km² area of Khanewal in Southern Punjab of Pakistan. The x‐y plots and maps of D‐Z parameters were produced to establish a decipherable vision for the occurrence and distribution of different water‐bearing formations of fresh‐saline water aquifers through a complicated situation of intermixing of different resistivity ranges for fresh‐saline water bodies. This technique is useful to reduce the ambiguity produced by the process of equivalence and suppression which cause intermixing in differentiating fresh, brackish, and saline aquifers during interpretation. The fresh‐saline water interface is correlated very well with the previous studies of water quality analysis carried out in Khanewal area. The results suggest that the D‐Z parameters are useful for demarcating different aquifer zones. The behavior and pattern of D‐Z parameters with respect to occurrence and distribution of different water‐bearing formations were effectively identified and delineated in the study area.     

Geophysical Images of the North Anatolian Fault Zone in the Erzincan Basin, Eastern Turkey, and their Tectonic Implications

The collision between the Arabian and Eurasian plates in eastern Turkey causes the Anatolian block to move westward. The North Anatolian Fault (NAF) is a major strike-slip fault that forms the northern boundary of the Anatolian block, and the Erzincan Basin is the largest sedimentary basin on the NAF. In the last century, two large earthquakes have ruptured the NAF within the Erzincan Basin and caused major damage (M _s = 8.0 in 1939 and M _s = 6.8 in 1992). The seismic hazard in Erzincan from future earthquakes on the NAF is significant because the unconsolidated sedimentary basin can amplify the ground motion during an earthquake. The amount of amplification depends on the thickness and geometry of the basin. Geophysical constraints can be used to image basin depth and predict the amount of seismic amplification. In this study, the basin geometry and fault zone structure were investigated using broadband magnetotelluric (MT) data collected on two profiles crossing the Erzincan Basin. A total of 24 broadband MT stations were acquired with 1–2 km spacing in 2005. Inversion of the MT data with 1D, 2D and 3D algorithms showed that the maximum thickness of the unconsolidated sediments is ~3 km in the Erzincan Basin. The MT resistivity models show that the northern flanks of the basin have a steeper dip than the southern flanks, and the basin deepens towards the east where it has a depth of 3.5 km. The MT models also show that the structure of the NAF may vary from east to west along the Erzincan Basin.     

Helium and neon isotopes in the Imnaha Basalt, Columbia River Basalt Group: Evidence for a Yellowstone plume source

Helium, neon, and argon isotopic compositions were measured in two flows of the Columbia River flood basalt. The Imnaha Basalt has a ³He/⁴He ratio of 11.4 times atmospheric and ²⁰Ne/²²Ne and ²¹Ne/²²Ne ratios characteristic of a plume component. The measured ³He/⁴He is a lower limit, due to possible preferential ³He loss and/or addition of radiogenic ⁴He. A Wanapum Basalt flow, erupted approximately 2 Ma later in the waning stages of volcanism, has more MORB-like noble gases. The He, Nd and Sr isotopic compositions of these lavas suggest that the Columbia River basalts were derived from the Yellowstone plume head which contained both ‘high-helium’ plume material and entrained depleted mantle. As the eruptions progressed the plume component in the melting region was gradually diluted or replaced.     

Geophysical evidence of the Eastern Marginal Fault of the Cheb Basin (Czech Republic)

The western part of the Bohemian Massif hosts an intersection of two regional fault zones, the SW-NE trending Oh?e/Eger Graben and the NNW-SSE trending Mariánské Lázně Fault, which has been reactivated several times in the geological history and controlled the formation of the Tertiary Cheb Basin. The broader area of the Cheb Basin is also related to permanent seismic activity of M_L 3+ earthquake swarms. The Eastern Marginal Fault of the Cheb Basin (northern segment of the Mariánské Lázně Fault) separates the basin sediments and underlying granites in the SW from the Kru?né Hory/Erzgebirge Mts. crystalline unit in the NE. We describe a detailed geophysical survey targeted to locating the Eastern Marginal Fault and determining its geometry in the depth. The survey was conducted at the Kopanina site near the Nový Kostel focal zone, which shows the strongest seismic activity of the whole Western Bohemia earthquake swarm region. Complex geophysical survey included gravimetry, electrical resistivity tomography, audiomagnetotellurics and seismic refraction. We found that the rocks within the Eastern Marginal Fault show low resistivity, low seismic velocity and density, which indicates their deep fracturing, weathering and higher water content. The dip of the fault in shallow depths is about 60° towards SW. At greater depths, the slope turns to subvertical with dip angle of about 80°. Results of geoelectrical methods show blocky fabric of the Cheb Basin and deep weathering of the granite bedrock, which is consistent with geologic models based on borehole surveys.     

Geophysical imaging of a kaolinite deposit at Sylvan,Manitoba, Canada

A geophysical survey was performed at Sylvan, Manitoba, Canada (51°5′N, 97°22′W) to investigate a Lower Cretaceous kaolinite deposit. The deposit consists of zones of kaolinite, silica sand, and lignitic clay located in a series of channels formed during karsting of the underlying Palaeozoic bedrock and is covered by 3 to 5 m of glacial drift. The aim of the study was to identify cost-efficient electrical and electromagnetic (EM) geophysical methods for locating, mapping, and assessing this target. Methods applied included terrain conductivity (EM31), VLF-EM, time-domain electromagnetics (TEM), DC-resistivity, and shallow seismic refraction. The survey showed that EM methods offer a viable alternative to more expensive seismic reflection surveys in the investigation of small industrial mineral deposits. Comparison of the geophysical survey results with those of a drilling program indicated that VLF-EM and TEM were the best methods for delineating the kaolinite deposit. VLF-EM was the most cost-efficient method for delineating the kaolinite deposit over a ca. 10 ha area and for exploring for further deposits within several kilometers of the main site. Joint interpretation of the in-phase and quadrature response is required for increased reliability in identifying the major kaolinite-filled channels. The TEM method provided more detailed resolution of the deposit than VLF-EM and was the optimal method for assessing its thickness. However, TEM data acquisition is too slow and inefficient for reconnaissance mapping of 10 ha sites. EM31 surveying is useful for defining the palaeokarst surface and overburden thickness in areas surrounding the deposit but cannot be used reliably for mapping the kaolinite deposit itself. The combined geophysical survey results show the kaolinite deposit at Sylvan to be located in a channel which is 100 m wide and about 25 m deep. The deposit has a bulk electrical conductivity between 13 mS m⁻¹ and 25 mS m⁻¹ consistent with low cation exchange capacity values measured for the kaolinite. The palaeokarst surface surrounding the deposit contains a series of sinuous, discontinuous, depressions with a depth variations of several meters.     

Jebel Marra,a dormant volcano in Darfur Province,Western Sudan

The geology of the Tertiary-Recent Marra mountains is shown on photogeological maps and described using data from short field visits and from previous literature. The 200 km long mass is aligned N-S parallel to basement trends; it comprises a stratified complex 2000 m thick of olivine basalts, pyroclastics and trachytes. Coarse detrital deposits testify to concomitant erosion. The spectacular Deriba caldera contains a deep crater lake and associated hot springs and fumeroles. The Marra mountains lie at the intersection of two transcontinental tectono-volcanic zones, ENE from Cameroon to Red Sea and SSE from Libya to Kenya.     

The role of rifting in the evolution of the continental margin of Eastern Asia: Geophysical evidence

The role of rift processes is analysed in the structural evolution of the continental margins of Eastern Asia including the Indo-China Peninsula and North China plain. Paleoreconstructions were made for the Indo-China Peninsula to characterize individual stages of rifting covering the Late Cretaceous-Eocene, Oligocene-Middle Miocene and Late Pliocene-Early Quaternary epochs. The rifting of continental margins occurred synchronously with spreading processes in marginal seas, whereas the formation of rift structures in the North China plain was concurrent with the formation of a deep-water basin of the Philippine Sea. The development of asthenospheric diapire led to crustal extension and was responsible for the formation of rift structures in marginal seas and continental margins.     

Spatial Analysis of Airborne Geophysical Data Applied to Geological Mapping and Mineral Prospecting in the Serra Leste Region, Carajás Mineral Province, Brazil

The Serra Leste region, located in the northeast portion of Carajás Mineral Province (PA), hosts important chrome-PGE, Au–Pd–Pt, Cu–Mo–Au, iron, and manganese deposits and occurrences related to different geological settings. We present a regional prospective model with focus on PGE mineralizations based on airborne geophysics (magnetometry, gamma-ray spectrometry and time domain electromagnetometry) and geological data. Geological and geophysics data analysis indicate a plausible correspondence between areas with meta-mafic–ultramafic rocks and low values in gamma spectrometry, mainly for the thorium channel. The meta-ultramafic units of the complexes, the main host rock of the PGE mineralization, are well defined by analytic signal from the anomalous magnetic field and by the apparent conductance anomalies derived from the GEOTEM system. The combination of the derivative products with updated geological data of the Serra Leste region and PGE-Luanga deposit enable to establish a regional prospective model for PGE and the identification of new targets within the studied area.     

Palaeomagnetism,age, and geochemistry of the Denchai Basalt,northern Thailand

The Denchai Basalt of northern Thailand is part of a large continental alkalic basaltic province extending through Thailand into Laos, Kampuchea, and Vietnam. It covers an area of about 70 km² and consists of seven flows, all with reversed magnetic polarity. The uppermost flow has yielded an age of 5.64 ± 0.28 Ma by the K-Ar method. During the igneous activity, magmas were apparently erupted from only one vent area, but changed in chemical composition from “hawaiite” (transitional to continental tholeiite) to true hawaiite and then to basanite. The basanite is the probable source of gem-quality zircon and sapphire mined from placer deposits associated with the basalts.